Despite the beauty of the event, it does raise some serious questions about e-waste.

At the Tokyo Hotaru Festival, the sea of blue LED lights flowed past the Tokyo Sky Tree, a radio broadcast tower that was completed in 2011 and is now the second tallest structure in the world after the Burj Khalifa. The tower was flooded in blue light for the event, reflecting the LEDs in the river below. The event, which took place just a day after the emergence of the amazing ‘supermoon’ on Saturday, was a treat for shutterbugs, with some photographers producing stunning long exposure shots like this and this showing the LEDs streaming down the river. But perhaps the best view of the event was from the air, as captured in this photo.

The LED lights were charged using solar power, according to CNET. But as TreeHugger notes, despite the beauty of the event, it does raise some serious questions about e-waste. Organizers used nets to collect the floating LED bulbs downstream, but what will become of them now? Is there any good use for 100,000 8.5-centimeter-wide LED bulbs (other than heaving them in a river, of course)?